Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~Z~ OS8
This invention relates to the galvanizing of
;, steel strip.
~' ` i
Galvanized steel has been proposed to be used
- in the automotive industry to provide improved corrosion
resistance for specific components. Unfortunately, the
gloss of painted zinc surfaces and mild steel are difficult
~ to match. I
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It has, therefore, been proposed to provide the zinc
coating on the intendea inner surface only of the steel strip,
thereby allowing painting of the exterior steel metal surface i
ir ,~ in conventional manner.
. . .
Various suggestions have been made ~or producing I ~ -
a selectively galvanized product, but none to date has been`
entirely commercially satisfactory from an economic stand-
;, ~ point. Prior art suggestions have included electrolytic
zinc deposition on one side only of the steel strip, melt Z
.~J~ ~ .
coating of zinc on one side only o the steel strip using
sophistlcated mechanical coating apparatus, hot-diP
~ galvaniæing the~steel strip on both sides in conventional
?'."'~, 20 manner and subsequently removing the coating from one side of
the strip using acld, and providing some sort of barrier layer
~-~ on the side of the sheet on which zinc is not desired to
prevent wetting of that siae during the galvanizing of~i
steel strip, the barrier layer subsequently being removed
or left in contact with the steel strip, depending on the
coating concerned. I
In accordance with the present invention, there is
.... . .
~ provided in a method of galvanizing only selected areas of
: ..... " .
- a ferrous metal strip, the improvement which comprises
contacting surface areas of the strip not to be galvanized
. - . .
with a phosphoric acid solution to cause a spontaneous
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reaction to form a readily chemically strippable coating
of a composite comprising iron hydroxides and hydrated
iron phosphates non-wetting in molten zinc on the surface
areas not to be galvanized, and passing the so-treated
strip through the molten zinc with the coating in contact
with the molten zinc.
By forming the coating on the mild steel sur-
..
face, prior to gal~anizing, ~inc is prevented from being
adhered to the coated surface. The coating may be removed
immediately after galvanizing or may be left in contact
:
with the mild steel surface during storage for later
,
removal prior to finishing of the surface.
~ :
While the invention has particular applicability to
and will be described with particular reerence to the con-
tinuous galvanizing of one side only of mIld steel strip in a
continuous operation, the invention may be used for the ,~
selective galvanizing of desired areas of any form of
steel sheet or strip by the formation of the coating on
those areas of the steel which do not require galvanizing.
The present invention also lncludes in the continuous
galvanizing of steel strip wherein steel strip is continu-
ously cleaned, pickled, fluxed and galvanized, the
operations, after the pickling and before the fluxing, of
contacting one side only of the strip with an inorganic acid
medium containing phosphoric acid to form on the one side
only a coating comprising iron hydroxides and hydrated iron
phosphates, and washing the coating substantially free from
any excess unreacted inorganic acid medium, whereby, upon
the galvanizing, the coating on the one side and the side of
the strip opposite to the one side contact molten zinc, and,
after the galvanizin~, a continuous steel strip is formed
~ , .
having a galvanizing coating only on the side thereof oppositP
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to the one side.
The chemical form of the coating depends on the
nature of the aqueous treatment solution used. The
treatment solution includes phosphoric acid and treatment
therewith usually is-carried out under oxidizing conditions.
. .
The coating usually is composed of hydrated iron hydroxides
and hydrated iron phosphates. Other salts may be present
in the coating depending upon the cations present in the
treating solution.
-" 10 Owing to their ready availability and effectiveness,
phosphoric acid-containing treating solutions containing
about 5 to about 50 g/l of total phosphate are preferred.
The formation of the preferred coating layer in
accordance with this invention usually is achieved by con-
tacting the surface of the steel on which the coating is
to be formed with a phosphoric acid and sodium phosphate
solution having an acid pH at a temperature above about
140F.
Oxidizing agents, such as nitrites and chlorates,
, .
may be added to the treating solution to accelerate the
~ rate of coating deposition.
... . .
The treatment solution used preferably is a
diluted form of a commercially-available phosphate solution
; j
concentrate, such as a Parker "Bonderite"*a Pennwalt '
"Fosbond"* an Amchem "Granodine"*or an Enthone "Enthox".*
The contact time depends on the weight of the
coating desired, the mode of contact used and in any event
is very short. The coating usually has a weight of less
than about 50 mg/sq.ft. of surface, preferably in the range
of about 20 to 40 mg/sq.ft. Coating weights of this order
of magni~ude have been found to be satisfactory in prevent-
.
~; ~ * Tr~demarks
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- 108105B
ing wetting of the coated surface by molten zinc in the
galvani~ing step and hence, in preventing adherence of zinc
;) to the coated surface. Coating weights of this order of
, magnitude may be achieved by contact times of only 1 to
2 seconds at about 150F between the treatment solution and
the mild steel surface, using spray or dip application.
Where roll application is used, a more acidic
, .......................................................................... .
solution may be required to achieve the required coating
' weight.
The coating layer which is provided in this
~, invention is a composite of a hydrated iron phsophate and ;~
iron hydroxide, such as a
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composite of Fe3 (PO4)2. 8H2O and Fe(OH?3r particularly
in the proportions of about 60% of the iron phosphate and
40~ of the ferric hydroxide.
The coating layer may be removed from the galvanized
strip after conventional adhesion of zinc to the uncoated
surface and cooling to provide a clean steel surface in-
,~ distinguishable from the initial mild steel surface and
i .;
'' to which paint may be applied by conventional automobile
~ painting techniques.
`~ 10 Removal of the preferred composite layer is
.... - .
~ achieved in rapid manner by mild acid treatment thereof~
;:,
One preferred removal operation involves contacting the
,.~., ,
coating layer with dilute hydrochloric acid, such as about 1 to
` about 10~ HCL, pre~ably about 3 to 4% HCl, at an elevated temperature
in the range of about 110 to about 180F, preferably about
~ . . .
150 to about 160F. One beneficial side effect of the acid
... .
removal treatment is an apparent smoothing of the mild
steel surface, thereby providing an improved surface for
.: .
painting.
f 20 The ready and rapid formation and removal of the
. . .
coating layer and its effectiveness in pre~enting adhesion
of zinc to treated surfaces allows incorporation of the
:
',.!' treatment and removal operations into a conventional con-
x, tinuous steel strip galvanizing operation without the
necessity of expensive equipment, time-consuming operations,
... .
or significant disruption to the normal operating parameters
` of the operation.
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The sole Figure of the accompanying drawings is a
. ......... .
y schematic representation of a continuous steel strip
;~ 30 galvanizing operation utilizing the present invention.
~ ,...
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1081C~
Referring to ~he drawing, continuous mild steel
strip 10 is passed throilgh a one-side galvanizing line 12,
ty?ically at the speed of a conventional continuous galvanizing
lin.e, to form a zinc coating on one side only of the steel
strip. The majority of the operations carried out on the
steel strip are conventional to continuous galvanizing oper-
ations and will be familiar to those skilled in the art,
including cleaning the strip by successive passage through a
hot al~aline bath 14, spray rinser 16, acid pickling bath 18
and spray rinser 20 and galvanizing the cleaned strip by
successive passage through a fluxing bath 22, a preheating
;;. ~ .
i chamber 24, a galvanizing bath of molten zinc 26 and a cooling
chamber 28. Conventional components and operations are used
and further description thereof is unnecessary.
. In accordance with the present invention, modifica- -
tions are made to the conventional continuous galvanizing line
to ensure the application o~ the zinc coating to one si~!
only of the steel strip 10, in place of the conventional
... . .
two-side application. Thus, immediately after rinsing in
spray rinser 20 and before fluxing in the fluxing bath 22,
the steel strip 10 passes through a preheater 30, which may
be in the form of a bath of hot ~ater, such as at a tempera-
ture of about 200F. Alternatively, the preheater 30 may
be in the form of a hot water spray applicator, and may
`' also fulfil the purpose of rinsing, thereby eliminating the
need for spray rinser 20.
: Thereafter, the preheated strip passes through a
treatment chaS~ber 32 wherein it is treated with acid solution
to form a coating of a composite or a barrier coating on the
side which is not required to be galvanized, such as by
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spray application with diluted Parker 901 concentrate.
Residual surface liquid from the treatment solution
application is removed by air doctors or rubber wringer rolls
34 prior to passage of the coated strip to the fluxing opera-
tion. Following application of the flux to the non-treated
side of the strip by sparger 36, excess flux flows into
; ~
collecting tank 38, and flux runaround at the edges and any
residual solution from the treatment is removed from the
: !
i barrier-coated side by spray washer 40.
~ ,
Following passage of the strip 10 through the
galvanizing bath 26 and the cooler 28, the metal strip,
which now has zinc coated on one side and the coating layer
coating on the other side, passes through a coating layer
stripper 42 wherein dilute hydrochloric acid contacts the
coating layer, to remove the coating layer~ The strip is
rinsed and then passes through a drier 44 to remove
residual moisture.
Application times of the steel strip 10 in the
;i
~j treatment chamber 32 and the coating layer stripper 42 are
,,~ 20 very short at the conventional speed of a galvanizing line,
.. j
;1 typically up to about 2 seconds, but these contact times
are effective for the formation and removal of the coating
,. . .
, layer.
Following the drying of the strip 10 in drier 44,
.i I
the strip may be coiled for shipment and use. If it is
desirea to ship the strip with the coating layer in contact
' therewith, the strip 10 may be coiled as it exits the cooler
r, j
,1 28. Roller levelling may be practised just prior to coilinq
~ in order to decrease the yield point elongation of the
'',:'1
; 30 steel.
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` ~IL08~C~S~
, . . . .
The mild steel surface of the one-side galvanized
strip resulting from this operation is physically indis-
tinguishable from the initial strip, and reacts identically
to normal cold rolled steel with respect to painting pre-
treatments, such as zinc phosphating, indicating that the
operations of formation of the coating and subsequent
removal thereof do not adversely affect the mild steel
surface.
This invention, therefore, permits the formation
~j 10 of one-side galvanized steel sheet suitable for automotive
use in-a convenient manner. External mild steel surfaces
in automobile components formed from such sheet may be
painted in conventional manner, with good matching with
other painted mila steel surfaces.
The invention is illustrated by the following
Examples:
Example 1
;-. i . .
~ Steel panels measuring 3 inches by 8 inches and. i
having a thickness of 0.033 inches were initially prepared
, . . .
, 20 by the following successive operations:
,r,~' i) degreased using condensing trichloroethylene;
;l ii) cleaned by dipping in an alkali cleaner,"Oakite 20",*.j .
~-, at 180F and at a concentration of 30 g/l for about 5
,~, seconds;
-;~ iii) rinsed in hot water at 170F for about 3 seconds;
,;;l iv) pickled in 12% by weight hydrochloric acid at room
r', ~ temperature; and
,~ v) rinsed in water under various conditions.
* Trademark
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-` 3L0810SE~
Thereafter, coatings were ~ormed on the panels by
application of various treating solutions for short periods
~; of time, followed by rinsing of the panels at 140F for
about 6 seconds. In each case, the coatings were found to
consist of hydrated iron compounds
:' .
Following measurement of the thickness of the
~ coating layer, the uncoated side then had a zinc ammonium
;~ chloride fluX applied thereto in a CQnCentratiOn of 75 g/l
at 180F.
After drying the fluxed panels at 450F for 30
seconds, the panels were dipped in a zinc bath having an
~` aluminum concentration of 0.12~ by weight at 860F forabout 10 seconds to form a zinc coating on the untreated
side. Thereafter, the panels were examined for adhesion
; of zinc to the initially coated side.
, .;
c Thereafter, the galvanized panels having a tempera-
ture of 200F were treated with 2~ by weight hydrochloric
~;~ acid at a temperature of 160F for about 5 seconds. After
i' '
- rinsing and drying, the galvanized panels were observed and
:
found to have one side coated with zinc and the other side
;` exhibiting a mild steel surface substantially indistinguish~
able from the intial surface. `
. '~
: ` The results of the various tests are reproduced in
:,
the following Table:
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The results of the above Tahle demonstrate that,
under la~oratory test conditions, coatings consisting of
hydrated compounds are effective in preventing zinc from
adhering to non-fluxed surfaces and are readily removed
after galvanizing. In particular, the coatings produced
` from Parker 901 are very effective at coating weights of
about 25 to 30 mg/ft.2.
; Example 2
Steel o~ commercial bottle top grade was batch
annealed, temper rolled to a #5 finish without oiling and
~ then slit into coils having a strip width of 12 inches.
^` This material was fed continuously to a pilot plant pro-
cessing line at a rate of 60 ft./min.
The processing received by the steel strip in the
i~ line consisted of the following sequentlal steps:
i) alkaline cleaning using "Oakite 2~" at 180F and
~' at a concentration of 36 g/l for 12 seconds;
;~l ii) cold water rinsing for about 4 seconds;
~`, iii) pickling in hydrochloric acid at 70F at a
,, ,
' 20 concentration of 12% by weight for about 6 seconds;
;~ iv) cold water spray rinsing for about 4 seconds;
v) hot water dipping at 200F for 7 seconds;
- vi) dipping in Parker 901 Bonderite solution at 160F
, I
I and at a concentration of 11.8% by volume for about 1.5
seconds, with appropriate masking to treat one side only
of the strip;
vii) air wiping of excess solution from the surface
~! and drying with hot air at a temperature of about 250F. The
time between dipping in the solution and complete drying of
i:~:' :
the coating was about 6 seconds;
viii) zinc ammonium chloride fluxing of the nontreated
.,.~,
~j side by use of a low pressure spray at a concentration of
' 'I :
I 75 g/l and a flux temperature of 185F;
1 1
, . .:- ::
L6~5~
ix) spray rinsing of the non-fluxed side at a water
flow rate of about 2 imp.gallons/min. and a water tempera-
ture of 118F;
x) air wiping of both sides and drying with hot air
at about 250F for about 4 seconds;
- xi) heating the steel to about 450F in an electrically
heated oven in about 18 seconds;
xii~ dipping in molten zinc containing 0.12% aluminum
at a temperature of 860F for about 4.8 seconds;
::: .
xiii) wiping both sides of the strip upon emerging from
the zinc bath with steam superheated to a temperature of
500F;
` xiv) cooling and solidifying the zinc coating using
., ~
cold air impingement for 7 seconds;
. .
/~ xv) stripping the non-zinc coated side by contacting
, .
' the surface with 2% by weight hydrochloric acid at a
~-j, temperature of 140F for 2 seconds, with minimization of
, attack of zinc coated side by the hydrochloric acid;
^~ xvij cold water spray rinsing of both sides before the
.. . .
20 acid wet strip dried for a total spray time of 5 seconds;
-I xvii) air wiping and hot air drying of the strip at a
temperature of about 250F for 4 seconds, and
~, xviii) recoiling of the strip.
The above-described sequence of process steps
~, resulted in a zinc free surface of mild steel and zinc
coated side having conventional hot dip galvanize spangle
,.'1
i characteristics. The zinc coating had excellent adhesion
' and coating weights were in the range of 0.26 to 0.46
i oz/ft. . The zinc coated side had bare edges of up to
0.25 inches.
12
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3lOSI~
The non-zinc coated side was found to react
identically to normal cold rolled steel with respect to
painting pretreatments, such as zinc phosphating. The
surface finish of the non-zinc coated side was not found
to have significantly altered during the process.
Therefore, in continuous pilot plant operation,
the coating rapidly produced from Parker 901 on the mild
steel surface effectively prevents the galvanizing of the
so-treated side of the steel strip. The coating was readily
~; 10 removed from the one-side galvanized strip and the coatingand subsequent removal operations did not adversely affect
the mild steel strip surface.
;; Example 3
:.
The procedure outlined in Example 2 was
repeated, except that in this instance the pretreatment step
~vi) was omitted.
The non-fluxed side of the strip was found to
,
have a generally spotty zinc pick up with a zinc coated
edge of approximately 0.5 to 0.8 inches in width.
Thus, ~hen the non-fluxed side of the sheet is
left bare, sporadic pick up of zinc occurs, which is
;: I
- considered unsatisfactory where a wholly mild steel
. . .
~; surface is required on the non-galvanized side.
Example 4
. , .
; The procedure outlined in Example 2 was repeated
on a commercial galvanizing line of the Cook-Norton design.
.,,
Steel strip of up to 38 inches in width and 0.042 inches
in thickness was processed on this line.
.~
In this instance, however, the treatment solu-
tion was applied by transfer from a rubber roller and the
-. solution had the composition used in Run 9 of Example 1.
~ - 13
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~0~ 58
A minimum elapsed time of 5 seconcl~; before rinsing was
allowed with no force drying during this period.
The steel strip produced thereby exhibited
similar properties to the steel strip processed in
Example 2, except that the edge effect on the zinc-coated
` side tended to be more variable, ranging from 0 up to 3
` inches.
The coa~ing applied, therefore, was very effec-
tive in preventing galvanizing of the so-treated side of
the steel sheet under continuous production line conditions.
The coating was readily removed following completion of the
.~ galvanizing.
`~ It is possible, therefore, to incorporate the
~ coating and removal operations into a conventional
^~ commercial galvanizing line and obtain one-side galvanized
mild steel strip without affecting the speed of operation 1
of the galvanizing line.
'
^ The present invention, therefore~ provides a
convenient and simple-to-use procedure for formation of
zinc coatings on selected surfaces only of mild steel. `
Modifications are possible within the scope o~ the inven-
. ~ ,
tion.
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